I seem to recall that several years ago people were discussing this type of brake failure
There’s a brake place in California that replaces pads, and I have no doubt that they would secure the pads properly. Alternatively, brass rivets or aluminum rivets along with high temperature adhesive would probably resecure the pad that came apart.
I would consider changing each and every pad front and back because they are all currently suspect if they came from the same shipment and the same lot number